1. Field of the Invention
This invention relates to a write device for an optical printer using the principle of a vacuum fluorescent tube, and more particularly to an optical write device of the type that a vacuum fluorescent tube having luminous dots obliquely arranged in a plurality of rows is operated according to a dynamic drive system.
2. Description of the Prior Art
Printers are generally divided into several types depending on a printing system. As non-impact type of the printer, an optical printer is known in the art, which exhibits an excellent print speed.
An optical printer, as shown in FIG. 1, generally comprises a write head for writing a print pattern and an electrophotography section for printing the pattern on a print paper. The optical printer includes a photosensitive body 1 such as, for example, a photosensitive drum or a photosensitive belt which is rotated at a predetermined speed in a direction indicated at an arrow, and an electrifier 2 for uniformly electrifying a surface of the photosensitive drum 1 and an optical write head 3 for applying a light pattern on the surface of the photosensitive drum 1 to form a latent image thereon which are arranged around the photosensitive drum 1. The optical printer also includes a developing device 4 for carrying out the application of toner depending on the electrification of the photosensitive drum 1 and a decalcomania or transfer heater 9 for adhering the toner onto decalcomania paper 9 fed from a cassette 7 after the photosensitive drum 1 passed through the developing device 4, to thereby carry out the transfer. Further, the printer includes an erasing lamp 5 for erasing electric charges remaining on the photosensitive drum 1 after the transfer and a cleaning blade 6 for removing toner from the photosensitive drum after the transfer.
Conventionally, a laser beam type head, a head having LED (light-emitting diode) dots arranged in an array, a combination of an LCD (liquid crystal display) shutter cell and a light source, or the like has been used as a write head for such an optical printer. Also, an optical write head has been recently developed which uses a vacuum fluorescent tube which is simple in structure and is capable of emitting light of a wavelength suitable for writing on a photosensitive drum.
However, the laser beam type write head is disadvantageous in that it is complicated and large-size in structure and also it is expensive, because it has a mechanically movable section, although it accomplishes writing at a high speed. The write head using an LED, LCD or vacuum fluorescent tube can be smaller in size, because it is free of any mechanically movable section, however, it is required to narrow intervals between adjacent luminous dots in order to improve resolution. Also, it has further disadvantages that the number of rows of luminous dots is increased corresponding to a variation of size of decalcomania paper and luminous control of the luminous dots must be carried out every luminous dot. Accordingly, the static drive of the write head requires drive circuits corresponding in number to the luminous dots, and an arrangement of the lead wires is highly troublesome.
In order to eliminate the above disadvantages of such a luminous array type write head, a write head has been proposed which is constructed to arrange luminous dots in at least two rays to control the luminous dots according to a dynamic drive system.
For example, FIGS. 2 and 3 show a vacuum fluorescent tube which has been proposed by the inventors and is adapted for use in a write head for the optical printer.
The vacuum fluorescent tube shown in FIGS. 2 and 3 includes a substrate 11 made of an insulating material such as glass or the like and having a plurality of stripe-like anode conductors 12 (eight in this instance) arranged thereon. The anode conductors 12 each have a phosphor layer 13 deposited thereon to form a luminous dot. The vacuum fluorescent tube also includes a plurality of control electrodes 14 arranged above the anode conductors 12 and each formed with a slit 15 obliquely across the phosphor layers. The control electrodes 14 are electrically independent from one another and led out to external terminals 16. Stretched above the control electrodes 14 are a plurality of filamentary cathodes 17 which are adapted to emit electrons when they are heated. These electrodes are sealedly enclosed in an airtight casing comprising side plates 18 and a front cover 19 and sealed on an periphery of the substrate 11, thereby to form the vacuum fluorescent tube.
The vacuum fluorescent tube of FIGS. 2 and 3 to be operated according to a dynamic described above can be decreased in the number of external terminals to about one eighth as many as the fluorescent tube of the static driving type. For example, supposing that printing is to be carried out at resolution of 12 lines/mm on paper of size B4 having an effective print width of 256 mm, it is required to arrange 3,072 luminous dots in a row and carry out luminous control using 3,072 external terminals in the vacuum fluorescent tube of the static drive type, whereas in the vacuum fluorescent tube of FIGS. 2, 3, 3,072 luminous dots can be controlled hy means of only 384 (3,072/8)+8 external terminals.
However, when the dynamic drive of the vacuum fluorescent tube shown in FIG. 2 is carried out in a manner to supply a scan signal to the control electrodes and supply a write signal to the anode conductors 12 in synchronism with a timing of scanning of the control electrodes 14, it exhibits the following disadvantages.
First, the photosensitive drum 1 shown in FIG. 1 must be constructed to be continuously rotated because of its mechanism. In other words, a rotational speed of the drum 1 cannot be decreased to keep a print speed at a predetermined level. Accordingly, in order to carry out the writing of one line substantially parallel to an axis of the drum 1, it is required to shorten a period of scanning the control electrodes and carry out the scanning of 384 control electrodes during a short period of time. Accordingly, luminous time of the luminous dot is substantially decreased, resulting in failing to provide luminance necessary for writing.
Also, the scanning of the control electrodes is disadvantageous in that it makes an order of transfer of write data to the anode conductors complicated. Further, the formation of a latent image on the photosensitive drum using the vacuum fluorescent tube shown in FIG. 2 fails to form a desired print pattern unless a print data array order is converted when the print data is input to the vacuum fluorescent tube, because the vacuum fluorescent tube fails in a correspondence between the array of luminous dots of the vacuum fluorescent tube and a print pattern on paper. Conversion of the print data array order is further troublesome when the vacuum fluorescent tube is operated according to the dynamic drive system.
In view of the above, it has been highly desirable to develop a data array conversion system effective for the application of print data to a printer head for the purpose of putting a printer head of the luminous dot array type to practice.